Analog solution of laser retinal coagulation

A mathematical calculation of the extent of retinal coagulation which results when a focused laser beam is incident on the retina, is described. For the chosen model of the eye an analytic solution of the diffusion equation was not possible; however, a resistance-capacity analog enabled the temperature distribution as a function of time to be obtained and, assuming a definite coagulation threshold (70°C), enabled the volume coagulated to be predicted. Isotherms corresponding to peak temperatures of 70°C are presented which show the extent of coagulation as a function of beam energy and beam defocusing.